Abort keystroke sequence?

When using Vim I sometimes find myself midway through entering a key combination and change my mind or realise it's incorrect (I'm still learning).

For example I may have typed d, 4 and be about to press d in order to delete 4 lines开发者_如何学编程 and realise this is not what I want to do. How can I abort the current sequence of keystrokes?

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Press ESC.

(no more text)

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Ctrl+C also aborts the current command.

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I prefer CTRL+[ over escape at all times, including aborting the current command. It's quicker and easier to type, particularly if you remap caps lock to ctrl.